1. Field of the Invention
The present invention relates to a focus adjustable apparatus.
2. Description of the Related Art
The visual system in humans allows individuals to assimilate information from the environment. The act of seeing starts when the lens of the eye focuses an image of its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of patterns of light into neuronal signals. Then, the neuronal signals are processed by the brain and humans therefore see what they are seeing.
A refractive error, or refraction error, is an error in the focusing of light by the eye. The refractive error comprises different types, such as myopia, hyperopia or astigmatism. Myopia refers to a refractive defect of the optical properties of an eye that causes images to focus on a forward portion of the retina (i.e., a refractive error). Those optical defects are typically caused by, among other things, defects of the cornea, elongation of the eye structure, other conditions, or a combination of those conditions. Hyperopia, on the other hand, refers to a refractive error of the optical properties of an eye that causes images to focus on a portion behind the retina. Those optical defects are the result when the optics of the eye is not strong enough for the front to back length of the eye. Astigmatism refers to a refractive error that causes light entering the eye to focus on two points rather than one. It is caused by an uneven power of the cornea. Myopia, hyperopia, and astigmatism are the principle refractive errors that cause persons to seek treatment to correct their vision problems, but there is still no treatment that can deal with these problems at one time except for laser vision correction.